As the semiconductor industry has progressed into nanometer technology process nodes in pursuit of higher device density, higher performance, and lower costs, challenges from both fabrication and design issues become greater. Lithography operations are one of the key operations in the semiconductor manufacturing process. In the lithography operations, flatness or unevenness of the underlying structure is important because of a tight focus margin in the lithography operations. Accordingly, it is necessary to planarize uneven underlying structures.